Astronomers have witnessed the most distant cosmic explosion on record: a gamma-ray burst that has come from the edge of the visible Universe.

Gamma-ray bursts are intense flares of high-energy radiation that appear without warning from across the cosmos.

They can release as much energy in a few minutes as our Sun will emit in its expected 10-billion-year lifetime.

The blast was observed by the Swift space telescope and by a number of ground-based observatories.

This is an amazing result that will enable us to find out more about stars from near the beginning of time

Keith Mason, chief executive PParc

The latest, record gamma-ray burst was detected on 4 September, 2005, and lasted about three minutes. It probably marked the death of a massive star as it collapsed into a black hole.

It has a redshift of 6.29, which translates to a distance of about 13 billion light-years from Earth.

The word redshift refers to the measure astronomers use to describe the way light coming from far-distant objects is "stretched" by the expansion of the Universe.

The higher the redshift number assigned to an object, the more distant it is and the earlier it is being seen in cosmic history.

Record distance

"This burst smashes the old distance record by 500 million light-years," said Dr Daniel Reichart, of the University of North Carolina, US, who has been leading the measurement of its distance.

The blast probably marked the death of a massive star

Professor Keith Mason, chief executive of the UK's Particle Physics and Astronomy Research Council (PParc), which helped fund Swift, commented: "This is an amazing result that will enable us to find out more about stars from near the beginning of time."

By studying objects at this distance, astronomers are looking into the Universe's early times. The burst comes from an era soon after stars and galaxies first formed, about one billion years after the Big Bang.

Dr Nial Tanvir, of the University of Hertfordshire, UK, who is an investigator on the Swift mission, said the telescope could yet spot more distant bursts hailing from even earlier stages in the Universe's evolution.

"I think you could see them at about 200-300 million years after the Big Bang. We don't know whether there were any stars at that time, but we should be able to see them at that distance if there were," he told the BBC News website.

Window on the past

The early Universe was smooth and homogeneous, a contrast to the clumpy array of galaxies and clusters observed today.

Observing events like this on the far edges of the visible Universe can help astronomers understand how this evolution took place.

It is thought that only the elements hydrogen and helium were produced by the Big Bang - everything else was "cooked up" by the first stars.

These early stars may have been quite different from those that exist today - for example, some researchers think they may have been much more massive.

"We can get an idea about that by looking at the debris they produced after exploding," said Dr Tanvir.

Scientists on four continents, using a variety of telescopes, have been tracking the burst and its afterglow as it gradually faded.

Astronomers plan to use the Hubble Space Telescope for observations at the end of the month, although the burst will have dimmed substantially by this time.